Transport system and transport method

ABSTRACT

A transport system includes a first track that passes above loading ports of the processing devices, and an overhead travelling vehicle that travels along the first track and includes a hoist. A second track is below the first track, passes above the loading ports, and is disposed in parallel or substantially in parallel with the first track. A buffer is provided below the second track at a position higher than the loading ports, and is arranged such that the articles can pass in a vertical direction over the loading ports. The buffer is disposed such that the articles can pass through the height position of the buffer in a vertical direction over the loading ports. A local vehicle travels along the second track and includes a hoist to perform delivery and receipt of the articles between the buffer and the loading ports.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transport system, and in particularto a transport system that supplies and removes articles without causinga processing device to wait.

2. Description of the Related Art

There is need for articles such as FOUPs (sealed cassettes fortransporting semiconductor wafers) to be supplied to and removed fromthe loading ports of devices such as a semiconductor machining deviceand a semiconductor inspection device without causing such devices towait. For this reason, it has been proposed to provide a buffer in thevicinity of a processing device, and provide a second transport devicefor performing transport between the buffer and the processing device.For example, in JP 2006-224944A, multiple overhead travelling vehicletracks are disposed in parallel in a ceiling space, one of which is usedfor long-distance transport, and another of which is used forshort-distance transport. A buffer is disposed under the track forlong-distance transport, and the loading port of a processing device isdisposed under the track for short-distance transport. The overheadtravelling vehicle for long-distance transport performs the delivery andreceipt of articles with the buffer, and the overhead travelling vehiclefor short-distance transport performs the delivery and receipt ofarticles between the buffer and the loading port. Accordingly, ifarticles required by the processing device have been transported to thebuffer in advance, the articles can be quickly supplied to theprocessing device. Also, the overhead travelling vehicle forshort-distance transport quickly removes articles from the loading portof the processing device. However, this configuration requires providingtracks at the same height position in parallel, thus increasing thefloor space occupied by the transport system in a plan view.

In JP 2005-150129A, a buffer including a transport device is provided infront of a processing device, an overhead travelling vehicle performsthe delivery and receipt of articles with the buffer, and the transportdevice of the buffer performs the delivery and receipt of articles withthe loading port. However, a display for indicating the operation state,an operation panel for manual operation, and the like are provided onthe front surface of the processing device, and it is not preferable forthem to be blocked by the buffer. Also, the loading port is used notonly by an automatic transport device, but also for manual supply andremoval of articles, and manual access is difficult if the front surfaceof the processing device is covered by the buffer.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a transportsystem and method that swiftly supply articles to and remove articlesfrom a processing device without blocking the front surface of theprocessing device, while significantly reducing the amount of floorspace occupied by the transport system in a plan view.

Another preferred embodiment of the present invention provides aspecific configuration of a local vehicle.

Also, various preferred embodiments of the present invention eliminatethe need for a local vehicle feeding line.

In addition, preferred embodiments of the present invention detect theexistence of a local vehicle under an overhead travelling vehiclewithout an additional device.

A transport system according to a preferred embodiment of the presentinvention transports an article between a plurality of processingdevices, and includes a first track that passes above a loading port ofa processing device; an overhead travelling vehicle that travels alongthe first track and includes a hoist; a second track that is below thefirst track, passes above the loading port, and is disposed in parallelor substantially in parallel with the first track; a buffer forplacement of the article, the buffer being provided below the secondtrack at a position higher than the loading port, and being arrangedsuch that the article can pass in a vertical direction over the loadingport; and a local vehicle that travels along the second track andincludes a hoist to perform delivery and receipt of the article betweenthe buffer and the loading port.

According to this preferred embodiment of the present invention, thespace where the overhead travelling vehicle travels and the space wherethe local vehicle travels can be vertically overlapped with each other.This enables a significant reduction in the amount of floor spaceoccupied by the transport system in a plan view. Also, the front surfaceof the processing device is not blocked by the buffer. Furthermore, theoverhead travelling vehicle and the local vehicle can both perform thedelivery and receipt of articles with the buffer and the loading port inboth directions. Accordingly, the processing device is not caused towait, and articles can be swiftly transported from the processingdevice. The buffer may be provided at only positions that are not overthe loading port, or a frame or the like of the buffer may be disposedover the loading port as well.

Another preferred embodiment of the present invention provides atransport system for addition on to an existing overhead travellingvehicle system including an overhead travelling vehicle in which a hoistis included and an overhead travelling vehicle track that passes above aloading port of a processing device. The transport system includes asecond track that is below the overhead travelling vehicle track, passesabove the loading port of the processing device, and is disposed inparallel or substantially in parallel with the overhead travellingvehicle track; a buffer for placement of an article, the buffer beingprovided below the second track at a position higher than the loadingport, and being arranged such that an article can pass in a verticaldirection over the loading port; and a local vehicle that travels alongthe second track and includes a hoist to perform delivery and receipt ofthe article between the buffer and the loading port.

This configuration enables the transport system including the secondtrack, the local vehicle, and the buffer to be added on to an existingoverhead travelling vehicle system. Also, the add-on transport systemdoes not require processing device modification, and even when appliedto an existing overhead travelling vehicle system, the add-on transportsystem only requires modification for the shared use of struts.

In various preferred embodiments of the present invention, delivery andreceipt of an article is performed between an overhead travellingvehicle in which a hoist is provided and a loading port of a processingdevice.

The overhead travelling vehicle travels along an overhead travellingvehicle track that passes above the loading port of the processingdevice, a second track is provided that is below the overhead travellingvehicle track, passes above the loading port of the processing device,and is disposed in parallel or substantially in parallel with theoverhead travelling vehicle track, a buffer for placement of the articleis provided below the second track at a position higher than the loadingport, and is arranged such that the article can pass in a verticaldirection over the loading port, a local vehicle is arranged such thatthe local vehicle travels along the second track and includes a hoist toperform delivery and receipt of the article between the buffer and theloading port, the overhead travelling vehicle performs a step forperforming delivery and receipt of the article with the buffer using thehoist; and the local vehicle performs a step for performing delivery andreceipt of the article between the buffer and the loading port.

Preferably, in the transport system according to a preferred embodimentof the present invention, the second track includes at least a pair ofrails, and a gap through which the article can pass in the verticaldirection is provided between the pair of rails. According to thisaspect of the present preferred embodiment of the present invention, thearticle can pass through the second track in the vertical directionsince, for example, the gap between the pair of rails of the secondtrack for supporting the local vehicle is preferably greater than thedepth of the articles. Accordingly, the first track, the second track,and the loading port can be disposed so as to vertically overlap eachother, and the article can be delivered and received easily. Also, thelocal vehicle can be supported by the pair of rails.

More preferably, in the transport system according to a preferredembodiment of the present invention, the first track, the second track,and the buffer are disposed in front of the processing device so as tooverlap with each other in parallel or substantially in parallel in planview, and the buffer is provided with a gap above the loading port, andthe overhead travelling vehicle and the local vehicle can performdelivery and receipt of the article with the loading port via the gap inthe buffer. This enables both the overhead travelling vehicle and thelocal vehicle to access the loading port.

Particularly preferably, in the transport system according to apreferred embodiment of the present invention, the buffer is disposed ata height according to which the local vehicle can pass above the bufferon which an article is placed in a case where the local vehicle istransporting an article. This enables the overhead travelling vehicleand the local vehicle to drop off an article at an arbitrary free spaceon the buffer, and remove an article from an arbitrary position.

Alternatively, the buffer may be disposed at a height according to whichthe local vehicle can pass above the buffer on which an article isplaced in a case where the local vehicle is not transporting an article,and the local vehicle cannot pass above the buffer on which an articleis placed in a case where the local vehicle is transporting an article.This configuration has the constraint of a sequence arising in thedelivery of articles to and removal of articles from the buffer by thelocal vehicle, but reduces the height difference between the buffer andthe second track, thus facilitating the installation of the buffer.

For example, a controller that is arranged and programmed to control theoverhead travelling vehicle and the local vehicle may be provided, andcontrol may be performed such that the overhead travelling vehicledelivers an article to the buffer and removes an article from theloading port, and the local vehicle delivers the article from the bufferto the loading port. According to this configuration, from the viewpointof the overhead travelling vehicle, the buffer becomes a loading portexclusively for the delivery of articles, and the loading port of theprocessing device becomes a loading port exclusively for the removal ofarticles, thus allowing prevention and minimization of the occurrence ofthe problem of not being able to deliver an article to a loading port.Also, from the viewpoint of the processing device, articles that are tobe processed can be accumulated on the buffer.

Preferably, the local vehicle is driven by a power storage member, and acharging device that charges the power storage member in the localvehicle is provided at a position along the second track that is locatedaway from a position over the loading port and away from a position overthe buffer. The power storage member may be a secondary buttery or acapacitor. This configuration enables charging of the battery of thelocal vehicle without hindering the delivery of articles to and theremoval of articles from the loading port and the buffer.

Alternatively, preferably the local vehicle is driven by electricalpower from the power storage member, and a charging device that chargesthe power storage member in the local vehicle is provided at each stopposition of the local vehicle along the second track. Since the localvehicle can be charged each time it stops, the local vehicle can bedriven by a battery or a capacitor such as an electric double layercapacitor, for example, and the capacity never has insufficient charge.

Preferably, the overhead travelling vehicle includes an opticalcommunication member that is at a position over the loading port andperforms optical communication with the loading port by light that has avertically-oriented optical axis and passes through a travelling path ofthe local vehicle. According to this configuration, when the localvehicle is positioned over the loading port, the overhead travellingvehicle cannot perform optical communication with the loading port.Accordingly, optical communication with the loading port can be used toeliminate the possibility of the local vehicle interfering with themovement of articles between the overhead travelling vehicle and theloading port.

Also, a controller of the local vehicle may be provided so as to be ableto communicate with the overhead travelling vehicle, the local vehicle,and the processing device. For example, the controller of the localvehicle communicates with the overhead travelling vehicle via optical orradio communication, and communicates with the local vehicle and theprocessing device via optical, radio, or wired communication. Thisallows the controller of the local vehicle to control the delivery ofarticles to and the removal of articles from the buffer and the loadingport.

Preferably, in the transport system, the buffer is provided with alook-down sensor to detect an interfering object on the loading portside. Here, the “loading port side” refers to the vicinity or theneighborhood of the loading port. Also, if the local vehicle and theoverhead travelling vehicle are controlled via the controller using thesignal from this sensor, it is possible to prevent an interfering objectsuch as a person in the vicinity of the loading port from interferingwith the operations of the transport devices, namely the local vehicleand the overhead travelling vehicle.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of relevant portions of a transport systemaccording to a preferred embodiment of the present invention.

FIG. 2 is a side view of relevant portions of a transport systemaccording to a variation of a preferred embodiment of the presentinvention in which the height level of a buffer has been changed fromFIG. 1.

FIG. 3 is a plan view of relevant portions of the transport systemaccording to a preferred embodiment of the present invention.

FIG. 4 is a plan view of relevant portions of the transport systemaccording to a variation of a preferred embodiment of the presentinvention.

FIG. 5 is a side view of a local vehicle.

FIG. 6 is a plan view of relevant portions of a variation in which alocal vehicle travels on a monorail.

FIG. 7 is a side view of relevant portions of a transport systemaccording to another preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes preferred embodiments of the present invention.The scope of the present invention is based on the claims, and isintended to be determined in accordance with the understanding of aperson skilled in the art with reference to the description of preferredembodiments of the present invention and related art in the field of thepresent invention.

FIGS. 1 to 7 show a transport system according to preferred embodimentsand variations thereof. In FIGS. 1 to 5, reference numeral 2 denotes anoverhead travelling vehicle that performs inter bay transport and intrabay transport in a semiconductor factory, for example. Reference numeral4 denotes a local vehicle that supplies articles 24 such as FOUPs to andremoves the articles 24 from individual processing devices 12, orsupplies articles to and removes articles from several adjacentprocessing devices 12. Reference numeral 6 denotes an overheadtravelling vehicle track that preferably includes travelling rails andan electricity feeding rail. Reference numeral 8 denotes a track for thelocal vehicle 4 that includes a pair of rails 9 shown in FIG. 3, forexample, and the articles 24 can vertically pass through the gap betweenthe rails 9. Although the local vehicle 4 is shown as traveling abovethe track 8, the local vehicle 4 may travel below the track 8. Theprocessing devices 12 each include one or more loading ports 14, and abuffer 10 and the tracks 6 and 8 extend in parallel or substantially inparallel in front of the processing devices 12. Reference numeral 16denotes the ceiling of a clean room or the like, and the tracks 6 and 8and the buffer 10 are supported by struts 17 to 19.

Reference numeral 10 denotes a buffer that is disposed below the track 8in parallel or substantially in parallel with the tracks 6 and 8, andthe buffer 10 is for the temporary placement of the articles 24. In thecase where an article 24 has been temporarily placed on the buffer 10,the local vehicle 4 travelling along the track 8 can pass over thebuffer 10 if it is not transporting an article 24, and cannot pass overthe buffer 10 if it is transporting an article 24. For this reason, ifmany articles have been temporarily placed on a buffer 10, a transportsequence arises when the local vehicle 4 transports articles 24 on thebuffer 10. In response to this, a configuration is possible in which, asshown in FIG. 2, the height level of the buffer 10 is lowered so as tobecome a buffer 11, thus enabling the local vehicle 4 transporting anarticle 24 to pass over the buffer 11 on which an article 24 has beentemporarily placed. For example, a gap that is greater than or equal totwo times the height of the article 24 is preferably provided betweenthe bottom of the track 8 and the top of the buffer 11. This enables theoverhead travelling vehicle 2 and the local vehicle 4 to drop off anarticle 24 at an arbitrary free position on the buffer 11, and remove anarticle 24 from an arbitrary position. The buffer 11 is preferably thesame as the buffer 10 with the exception of having a lower height level,and either the buffer 10 or the buffer 11 may be used in the presentpreferred embodiment.

The overhead travelling vehicle track 6 is at the highest position, thelocal vehicle track 8 is disposed under the track 6, for example, andthe tracks 6 and 8 vertically overlap each other in parallel orsubstantially in parallel. The buffer 10 or 11 is disposed under thetracks 6 and 8 in parallel or substantially in parallel with them, andthe loading ports 14 are disposed under the tracks 6 and 8. In the casewhere the buffer 10 or 11 and the loading ports 14 are disposed so as tooverlap each other in a plan view as in the present preferredembodiment, gaps 30 are provided in the buffer 10 and 11 over theloading ports in order for the articles 24 to vertically pass through.Alternatively, the buffer 10 or 11 may be arranged to avoid a positionthat overlaps the loading ports 14 in a plan view. The local vehicletrack 8 includes a charging device 20 at, for example, a position thatoverlaps neither the loading ports 14 nor the buffer 10 or 11 in a planview at one end of the track 8, and the charging device 20 charges thebattery of the local vehicle 4. Note that the charging device 20 may beprovided at a position that vertically overlaps an article 24 on thebuffer 10 or 11. However, this configuration results in interferencebetween the charging of the local vehicle 4 and the delivery and receiptof articles between the overhead travelling vehicle 2 and the buffer 10or 11. Accordingly, it is preferable that the charging device 20 isprovided at an end portion of the track 8, at a position that verticallyoverlaps neither the loading ports 14 nor the buffer 10 or 11.

Reference numeral 22 denotes a local controller that controls the localvehicle 4, and in the present preferred embodiment, the local controller22 is provided in the vicinity of the charging device 20 andcommunicates with the local vehicle 4 by optical communication or thelike. Note that the local controller 22 may be provided ground-side.Also, electricity is preferably supplied to the charging device 20 via afeeding line (not shown) provided along a strut 18, for example.

The overhead travelling vehicle 2 preferably includes safety covers 25in the front and rear, for example, to prevent an article from falling,and moves an article 24 in the vertical direction by raising andlowering an elevation platform 26 using a hoist (not shown). Theoverhead travelling vehicle 2 may be additionally provided with, forexample, a transverse feeding mechanism to transversely feed thearticles 24. The overhead travelling vehicle preferably includes anoptical communication unit 31, and interlocking before articledelivery/receipt is performed by optical communication between theoptical communication unit 31 and an optical communication unit 31′provided on the loading port 14 side, using light that has avertically-oriented optical axis and passes through the travelling pathof the local vehicle 4. Here, the optical communication units 31 and 31′are disposed such that the optical axis between the opticalcommunication units 31 and 31′ is blocked if the local vehicle 4 ispositioned between the overhead travelling vehicle 2 and the loadingport 14. This enables confirmation that the local vehicle is notpositioned between the overhead travelling vehicle 2 and the loadingport 14, without an extra device need to detect the local vehicle 4.Furthermore, the overhead travelling vehicle 2 is preferably providedwith a communication device (not shown) that communicates with the localcontroller 22, and communicates with the local controller 22 whendelivering articles to and receiving articles from the buffer 10 or 11.

Here, in addition to a machining device, it is assumed that aninspection device is included as a processing device 12. The loadingport 14 is provided on the front surface of the processing device 12,and the articles 24 are delivered to and received from the loading port14 by the overhead travelling vehicle 2, the local vehicle 4, and aperson moving on the ground. In addition to the loading port 14, thefront surface of the processing device 12 is provided with a display 28,an operation panel 29, and the like, thus enabling monitoring of theoperation state of the processing device 12 and manually controlling theprocessing device 12.

The local vehicle track 8 preferably includes the pair of rails 9, andthe width D (FIG. 3) between the rails 9 is greater than the depth ofthe articles 24, thus enabling the articles 24 to vertically passthrough the gap between the rails 9 along with the elevation platform26. Furthermore, the gap 30 is preferably provided in the buffer 10 or11 above each of the loading ports 14, thus enabling the articles 24 tovertically pass through the buffer 10 or 11. Alternatively, the buffer10 or 11 may be arranged so as to not be located over the loading ports14. For such reasons, even if the tracks 6 and 8 and the loading ports14 are disposed so as to vertically overlap each other, the overheadtravelling vehicle 2 can deliver articles to and receive articles fromthe loading ports 14 and the buffer 10 or 11. Similarly, the localvehicle 4 can deliver articles to and receive articles from the buffer10 or 11 and the loading ports 14. This enables minimizing of the floorspace occupied by the transport system in a plan view.

If the buffer capacity is insufficient with only the buffer 10 or thelike under the local vehicle track 8, an additional buffer 32 may beprovided and supported from the ceiling or the like by struts 34, asshown in FIG. 4. In this case, the additional buffer 32 is disposed atthe same height position as the buffer 10 or the like, and the overheadtravelling vehicle 2 and the local vehicle 4 are provided with, forexample, a mechanism that transversely feeds the hoist.

FIG. 5 shows the structure of the local vehicle 4, and the local vehicle4 travels above the rails 9 via running wheels 41 or the like due todriving of a running motor denoted by reference numeral 40. Referencenumeral 42 denotes a hoist that raises and lowers the article 24supported by the elevation platform 27, by winding up and reeling outsuspending members 43. Reference numeral 45 denotes a battery, referencenumeral 46 denotes a connector, and the battery 45 is charged by thecharging device 20. Reference numeral 47 denotes an opticalcommunication unit that performs communication to interlock with theoptical communication unit 31′ of the loading port 14, similarly theoptical communication unit 31 of the overhead travelling vehicle 2. Notethat a configuration is possible in which the optical communication unit47 is not provided, and interlocking with the loading port 14 isperformed via the local controller 22. The local vehicle 4 is a simplevehicle that has a short travelling distance, does not include amechanism for transverse feeding of articles or the like, and does notinclude an information processor for selecting a travelling route,avoiding interference with another vehicle, and the like. For example,one local vehicle 4 is caused to move back and forth between the frontof the processing device 12 and a position somewhat spaced away from thefront by travelling along the track 8, under control of the localcontroller 22. Also, the local vehicle 4 does not require additionalfloor space since it travels along the track 8 under the overheadtravelling vehicle track 6. Also, the articles 24 can be delivered andreceived by vertically passing through the track 8 since the gap Dbetween the rails 9 of the track 8 is greater than the depth of thearticles 24.

FIG. 6 shows a transport system according to a variation of a preferredembodiment of the present invention, and in this figure, the samereference numerals denote portions that are the same as those in FIGS. 1to 5, and the overhead travelling vehicle 2 is shown without the safetycovers 25. In this variation, a local vehicle track 8′ is preferably amonorail, for example. Although the cross-sectional shape of the track8′ is preferably L-shaped, for example, an arbitrary shape may be used.A local vehicle 4′ preferably includes three types of guide rollers 51to 53, for example, and the orientation of the local vehicle 4′ ismaintained due to the guide rollers 51 to 53 being guided by the track8′. The guide roller 53 need not be provided. Reference numeral 10′denotes a new buffer, in which the gaps 30 are provided, and thearticles 24 vertically pass through the gaps 30. In the variation shownin FIG. 6, the orientation of the local vehicle 4′ readily becomesunstable since the local vehicle 4′ is supported by a monorail.

The following describes control of the overhead travelling vehicle 2 andthe local vehicle 4 of the present preferred embodiment. The overheadtravelling vehicle 2 is controlled by a host controller (not shown), andthe local controller 22 performs communication with the host controller,the overhead travelling vehicle 2, and the local vehicle 4. When theoverhead travelling vehicle 14 and the local vehicle 4 deliver articles24 to and receive articles 24 from the loading port 14, interlocking isperformed using the optical communication units 31, 31′, and 47. Whenthe local vehicle 4 is positioned over the loading port 14, the overheadtravelling vehicle 2 cannot perform optical communication, andinterlocking is not established, and thus the delivery and receipt ofarticles is delayed until the local vehicle 4 moves to another position.When articles 24 are to be delivered and received between the buffer 10or 11 and the overhead travelling vehicle 2, or the like, interlockingis established through communication between the overhead travellingvehicle 2 and the local controller 22. Also, in accordance with aninstruction from the local controller 22, the local vehicle 4 performsthe delivery and receipt of articles 24 with the buffer 10 or the like,and interlocking before delivery/receipt is not performed.

Inventory data indicating at which positions which articles are placedon the buffer 10 or the like is obtained through the abovecommunication, and such inventory data is stored in the local controller22. The local controller 22 manages the articles 24 on the buffer 10 orthe like. Also, interlocking with the loading port 14 is establishedthrough direct communication with the overhead travelling vehicle 2 andthe local vehicle, or through communication via the local controller 22.

FIG. 7 shows another preferred embodiment of the present invention, andin this figure, the same reference numerals denote portions that are thesame as those in FIGS. 1 to 6. The preferred embodiment shown in FIG. 7is similar to the variation shown in FIG. 2, with the exception of thepoints mentioned in particular below. Reference numeral 60 denotes alook-down sensor that emits a laser beam and detects the laser beam withuse of a photoreception element when the laser beam has been reflectedby an interfering object such as a person. An interfering object insidethe monitoring range indicated by a chain line in the vicinity of theloading port 14 is detected by, for example, scanning the laser beamthrough changing its orientation, and using a phase difference betweenreflected light and the laser beam. A signal from the look-down sensor60 is transmitted from the local controller 22 to the local vehicle 4and the overhead travelling vehicle 2, and pick-up and drop-off from andto the loading port 14 is prohibited when an interfering object ispresent. Note that the type of sensor used to detect an interferingobject is arbitrary.

The charging device 20 is provided, for example, at each stop positionof the local vehicle 4 along the track 8, and the battery of the localvehicle 4 can be charged at an arbitrary one of such positions when thelocal vehicle 4 stops. Note that since it is not preferable for astandby position of the local vehicle 4 to be located over a loadingport 14, a configuration is possible in which the charging devices 20are not provided over the loading ports 14. Also, instead of a batterysuch as a lithium ion battery, it is possible to use a capacitor such asan electric double layer capacitor, for example.

The local controller 22 communicates with the overhead travellingvehicle 2 via optical or radio communication, and communicates with thelocal vehicle 4 and the processing devices 12 via optical, radio, orwired communication. Accordingly, interlocking can be established viathe local controller 22 when the overhead travelling vehicle 2 and thelocal vehicle 4 are to move articles 24 to and from the buffer 11 andthe loading ports 14.

The following describes an example of the operation of the transportsystem shown in FIG. 7.

The overhead travelling vehicle 2 drops off an article 24 onto thebuffer 11, and removes an article 24 from the loading port 14. Theprovision of the buffer 11 enables reducing the occurrence of theproblem of the overhead travelling vehicle 2 not being able to drop offan article 24, and allows the processing device 12 to keep a stock ofarticles 24 to be processed next on the buffer 11.

The local vehicle 4 delivers an article 24 from the buffer 11 to theloading port 14.

If there is the risk of an overflow of articles 24 at the loading port14, the local vehicle 4 removes articles 24 and delivers them to thebuffer 11.

An urgent article may be directly dropped off at the loading port 14 bythe overhead travelling vehicle 2.

The standby position of the local vehicle 4 is a position that is notover a loading port 14, and further is above an article that is next insequence to be dropped off at the loading port 14. This enables swiftdelivery of articles to the loading port 14.

The local vehicle 4 is charged at an arbitrary position while stopped.This enables driving of the local vehicle 4 with a low-capacity battery.

The local vehicle 4 picks up an article to be delivered to the loadingport 14 at the same time as the overhead travelling vehicle 2 removes anarticle from the loading port 14. This enables swift delivery of thenext article to the loading port 14.

If an article is to be delivered to the loading port 14, the overheadtravelling vehicle 2 that is transporting the article to be delivered tothe loading port 14 drops off the article at the buffer 11 that isupstream of the loading port 14, and subsequently the same overheadtravelling vehicle 2 removes an article from the loading port 14. Thisenables efficient transport of the articles.

The above preferred embodiment achieves at least the followingadvantages.

The buffer 10 and the like can be provided without blocking the frontsurface of the processing devices 12.

The tracks 6 and 8 are disposed so as to overlap each other in thevertical direction, and the articles 24 can pass through the gapprovided in the track 8, thus eliminating the need for a transversefeeding mechanism in the overhead travelling vehicle 2 and the localvehicle 4.

A buffer 10 or 11 having a sufficient capacity for the processingdevices 12 can be provided by lengthening the track 8.

The overhead travelling vehicle 2 and the local vehicle 4 can bothperform the delivery and receipt of articles with the loading ports 14and the buffer 10 or 11 in both directions. This enables efficientlysupplying of articles 24 to and removing of articles 24 from the loadingports 14 and the buffer 10 or 11.

Note that it is not necessary to provide all of the processing devices12 with the system made up of the buffer 10, the local vehicle 4, andthe track 8 for the local vehicle 4, and it is possible to provide sucha system to only process devices 12 that process a large number ofarticles 24. The type of transport article is arbitrary, and examplesthereof include a cassette accommodating a semiconductor exposurereticle, and a flat panel display substrate.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A transport system to transport an article among a plurality ofprocessing devices, the transport system comprising: a first track thatpasses above loading ports of the processing devices; an overheadtravelling vehicle travelling along the first track and including ahoist; a second track below and in parallel or substantially in parallelwith the first track, the second track passing above the loading port; abuffer for placement of the article, the buffer being provided below thesecond track at a position higher than the loading port, and beingarranged to allow the article to pass in a vertical direction over theloading port; and a local vehicle travelling along the second track andincluding a hoist to perform delivery and receipt of the article betweenthe buffer and the loading port.
 2. The transport system according toclaim 1, wherein the second track includes at least a pair of rails, anda gap through which the article passes in the vertical direction isprovided between the pair of rails.
 3. The transport system according toclaim 1, wherein the first track, the second track, and the buffer aredisposed in front of the processing device so as to overlap with eachother in parallel or substantially in parallel in plan view, the bufferis provided with a gap above the loading port, and the overheadtravelling vehicle and the local vehicle perform delivery and receipt ofthe article with the loading port via the gap in the buffer.
 4. Thetransport system according to claim 1, wherein the buffer is disposed ata height which enables the local vehicle to pass above the buffer onwhich the article is placed in a case where the local vehicle istransporting the article.
 5. The transport system according to claim 1,wherein the buffer is disposed at a height which enables the localvehicle to pass above the buffer on which the article is placed in acase where the local vehicle is not transporting the article, and thelocal vehicle cannot pass above the buffer on which the article isplaced in a case where the local vehicle is transporting the article. 6.The transport system according to claim 1, wherein the buffer includes alook-down sensor to detect an interfering object on a side of theloading port.
 7. The transport system according to claim 1, furthercomprising: a controller arranged and programmed to control the overheadtravelling vehicle and the local vehicle such that the overheadtravelling vehicle delivers the article to the buffer and removes thearticle from the loading port, and the local vehicle delivers thearticle from the buffer to the loading port.
 8. The transport systemaccording to claim 1, wherein the local vehicle is battery-driven, and acharging device to charge a power storage member in the local vehicle isprovided at a position along the second track that is located away froma position over the loading port and away from a position over thebuffer.
 9. The transport system according to claim 1, wherein the localvehicle is driven by electrical power from a power storage member, and acharging device to charge the power storage member in the local vehicleis provided at each stop position of the local vehicle along the secondtrack.
 10. The transport system according to claim 1, wherein theoverhead travelling vehicle comprises an optical communication memberthat is at a position over the loading port and is arranged to performoptical communication with the loading port by light that has avertically-oriented optical axis and passes through a travelling path ofthe local vehicle.
 11. The transport system according to claim 1,wherein a controller of the local vehicle is arranged to communicatewith the overhead travelling vehicle, the local vehicle, and theprocessing device.
 12. A transport system for addition on to an existingoverhead travelling vehicle system including an overhead travellingvehicle in which a hoist is included and an overhead travelling vehicletrack that passes above a loading port of a processing device, thetransport system comprising: a second track that is below the overheadtravelling vehicle track, passes above the loading port of theprocessing device, and is disposed in parallel or substantially inparallel with the overhead travelling vehicle track; a buffer forplacement of an article, the buffer being provided below the secondtrack at a position higher than the loading port, and being arrangedsuch that the article is capable of passing in a vertical direction overthe loading port; and a local vehicle that travels along the secondtrack and includes a hoist to perform delivery and receipt of thearticle between the buffer and the loading port.
 13. A transport methodfor performing delivery and receipt of an article between an overheadtravelling vehicle in which a hoist is provided and a loading port of aprocessing device, the overhead travelling vehicle travelling along anoverhead travelling vehicle track that passes above the loading port ofthe processing device, wherein a second track is below the overheadtravelling vehicle track, passes above the loading port of theprocessing device, and is disposed in parallel or substantially inparallel with the overhead travelling vehicle track, a buffer forplacement of the article is below the second track at a position higherthan the loading port and arranged to allow the article to pass in avertical direction over the loading port, and a local vehicle travelsalong the second track and includes a hoist to perform delivery andreceipt of the article between the buffer and the loading port, themethod comprising: a step for performing delivery and receipt of thearticle with the buffer using the hoist by the overhead travellingvehicle; and a step for performing delivery and receipt of the articlebetween the buffer and the loading port by the local vehicle.